Acquired immune deficiency syndrome (AIDS) is now recognized as one of the greatest health threats facing modern medicine. There is, as yet, no cure for this almost invariably fatal disease. This state of affairs has made the prevention of the disease an extremely high priority in the medical community. An individual who is infected with human immunodeficiency virus (HIV), the etiologic agent of AIDS, can transmit the disease, and yet remain asymptomatic for many years. The ability to accurately screen large numbers of asymptomatic individuals (e.g., healthy appearing blood donors) for HIV infection is of great importance. Furthermore, the development of a vaccine would be particularly desirable, since it would afford some protection against transmission of AIDS by individuals who either are not detected by a diagnostic test, or evade such a test.
In 1983-1984, three groups independently identified the suspected etiological agent of AIDS. See, e.g., Barre-Sinoussi et al. (1983) Science 220:868-871; Montagnier et al., in Human T-Cell Leukemia Viruses (Gallo, Essex & Gross, eds., 1984); Vilmer et al. (1984) The Lancet 1:753; Popovic et al. (1984) Science 224:497-500; Levy et al. (1984) Science 225: 840-842. These isolates were variously called lymphadenopathy-associated virus (LAV), human T-cell lymphotropic virus type III (HTLV-III), or AIDS-associated retrovirus (ARV). All of these isolates are strains of the same virus, and were later collectively named human immunodeficiency virus (HIV). With the isolation of a related AIDS-causing virus, the strains originally called HIV are now termed HIV-1 and the related virus is called HIV-2. See, e.g., Guyader et al. (1987) Nature 326:662-669; Brun-Vezinet et al. (1986) Science 233:343-346; Clavel et al. (1986) Nature 324:691-695.
Initially, HIV was propagated in culture in human mitogen-activated T cells. This method, however, could not produce the large quantities of virus required for serology assays on the scale required to protect public health and safety. It was not until immortalized cell lines capable of becoming chronically infected in vitro were discovered that HIV could be produced in any substantial quantities. See, e.g., Montagnier et al. (1984) Science 225:63-66; Levy et al., supra; Popovic et al., supra. The ability to grow the virus in culture led to the development of immunoassays for the detection of anti-HIV antibodies in the blood of patients suspected of having been infected, as well as for screening blood donors. See, e.g., Schupbach et al. (1984) Science 224:503-505; Sarngadharan et al. (1984) Science 224:506-508; Feorino et al. (1984) Science 225:69-72; Kalyanaraman et al. (1984) Science 225: 321-323; Culliton et al. (1984) Science 226:1128-1131; Groopman et al. (1984) Science 226:447-449; Ho et al. (1984) Science 226:451-453; U.S. Pat. No. 4,520,113.
Due to the great hazard of cultivating HIV in vitro, the number of facilities and individuals capable of working with the virus is necessarily limited. Furthermore, while tissue culture may provide viral polypeptides suitable for use in diagnostic assays, it is highly undesirable to employ polypeptides produced by tissue culture in vaccine compositions due to the risk of infectivity posed by live, intact virus.
While production of viral polypeptides by recombinant means could be considered to be a solution to the problems described above, the production of recombinant proteins was not possible prior to the present invention. For example, HIV nucleotide sequences were not available and sequenced so as to enable the production of recombinant proteins. Even more importantly, it was unknown whether recombinantly produced viral protein would be sufficiently similar in antigenic properties to native HIV polypeptides so as to be generally useful in diagnostic assays or vaccine production. In addition, homology between the genome of HIV and human T-cell leukemia virus type I and type II (HTLV-I and -II) had been reported. See, e.g., Arya et al. (1984) Science 225:927-930. Thus, it was unclear that sufficiently unique epitopes of HIV could be produced by recombinant means to distinguish HIV from HTLV-I or HTLV-II. Furthermore, it was unclear prior to the present invention whether the various HIV isolates possessed sufficiently related epitopes so that a recombinant polypeptide based on one isolate could be useful in a general diagnostic assay or vaccine composition.
Prior to the present invention, therefore, recombinant HIV polypeptides could not be produced and it was not clear that such polypeptides would be generally useful in diagnostic, prophylactic, or therapeutic methods or products.